The Impacts of Effective Diffusion on the Axisymmetrization Process

The dynamics of vortex axisymmetrization from the perspective of thermal anomalies is investigated using an idealized, nonlinear atmospheric model called HIGRAD. Attempts at reproducing the nonlinear modeling results of previous work (which used WRF, Nolan and Grasso 2003; NG03) revealed a discrepancy with the impacts of purely asymmetric forcing. The current study finds that linear, thermal asymmetries can have an important, largely positive role on the vortex intensification whereas NG03 find nearly the opposite. Absolute angular momentum budgets reveal that the likely reason for the differences with NG03 is the strength of the basic-state secondary circulation. Radial momentum budgets and sensitivity analysis further reveals that differences in effective diffusion between the two nonlinear models are likely the driving force behind these results.

Detailed comparisons between HIGRAD and WRF including kinetic energy spectra and idealized simulations that attempt to understand the differences in effective diffusion between the two models will be presented.